How Nerves Work Flashcards
Give the three subdivisions of the nervous system
- the brain
- the spinal cord
- peripheral nerves
What are the two subdivisions of the peripheral nervous system?
- sympathetic nervous system
- autonomic nervous system
Give the five components of the neurone
- cell body/soma
- dendrites
- initial segment
- axon
- axon terminals
What part of the neurone contains the nucleus?
Soma
At what part of the neurone is the information for making action potentials arranged?
Initial segment
What part of the neurone is an important route for the information from other neurones?
Dendrites
What part of the neurone takes the action potential elsewhere?
Axon
What part of the neurone connects with other nerves/muscles and releases neurotransmitter?
Axon terminals
What is the typical RMP of neurones?
around -70mV
What pumps are present in the cell membrane?
Sodium/potassium pumps
What do potassium specific ions channels in the membranes allow?
Potassium to flow out down the conc gradient through facilitated diffusion
The electrical gradient pulling the potassium back into the cell eventually becomes equal to the conc gradient pushing the ions out of the cell. This alone would create a resting potential of -90mV, so why is RMP closer to -70mV?
Due to the permeability of the membrane to other ions and leaky channels
How do neurones communicate?
Using action potentials
What are action potentials?
Large all or nothing signals that can self propagate
What needs to happen before an AP can be fired?
A graded potential must reach a significant level
Give features of graded potentials
- vary in intensity with intensity of stimulus
- decremental
- can only transmit over very short distances
- can be inhibitory or excitatory depending on which ion channels are open
- can summate through temporal or spatial summation
What happens once a graded potential reaches the correct threshold?
Action potential will be fired
- voltage gated sodium channels in the membrane open
- sodium rushes in
- this causes huge depolarisation of the neurone
- this in turn causes K+ channels to open
- cell repolarises then hyper polarises
What effect do these graded potentials have?
Change the potential of the neurone to around +40mV
Are action potentials graded or all or nothing?
All or nothing
Intensity of an AP is not shown in amplitude but instead by
frequency
Action potentials are
self-propagating, since the charge created by influx of Na+ ions spreads a bit up the axon, opening the channels there too, allowing further influx and propagation of the signal
What three types of nerve fibre are there and what are their functions?
Afferent (sensory) - detect changes or sensory stimuli
Interneurones - contained within the spinal cord, decide what to do about the stimulus
Efferent (motor) - if an excitatory response is warranted, these neurones carry the signal to the effector tissues or cells
Neurones can be ___ or ___,
and ___ or ___
large or small
myelinated or unmyelinated
Large axons allow for
a much faster transmission speed, since resistance is decreased
Faster transmission speed allows for
the charge to travel further up the axon when Na+ channels are opened, which in turn allows them to be placed further apart and less are needed
Since the most time consuming part is the opening of these channels, reducing the number needed
increases transmission time
Myelination also speeds up transmission by
surrounding the axon in a lipid sheath formed from Schwann cells (replaced by oligodendrocytes in the CNS)
Sodium channels are only found
in the nodes of Ranvier between these sheaths which allows the transmission to travel further due to the insulation provided
Give an example of a demyelinating disease
Multiple sclerosis
Describe the consequences of demyelinating disease
- eat holes in the Schwann cells
- results in rapid decay of APs
- preventing APs from reaching the next node and from propagating
- conduction falls
At the NMJ, the motor end plate from the neuronal axon comes to the muscle and
forms a synapse
On the muscle side of the synapse lies the
sarcolemma
The membrane of the sarcolemma has junctional folds with
ACh receptors, leading deeper into the muscle allowing for deeper contraction
Describe the process of neuromuscular transmission
- AP in axon opens Ca2+ channels in presynaptic terminal
- triggers fusion of vesicles and ACh is released into the cleft
- diffuses across and binds to receptors in the junctional folds
- ligand gated Na+/K+ channels are opened
- local end plate potential is produced which always reaches threshold so AP is fired, opening up voltage gated Na+ channels
- ACh is removed by acetylcholinesterase
Neuronal synapses are similar to the neuromuscular junctions, but the few differences make a huge amount of differences. List these differences
- wide range of neurotransmitters
- range of postsynaptic potentials
- anatomical arrangements of synapses
- synaptic connectivitty
Give the four types of postsynaptic potentials
- fast EPSPs
- slow EPSPs
- fast IPSPs
- slow IPSPs
Give the three anatomical arrangements of synapses
- axo-somatic
- axo-dendritic
- axo-axonal
Give the two types of synaptic connectivity
- convergence
- divergence
